Amphibians

Impacts of Pesticides on Amphibians

Amphibians can be indirectly exposed to pesticides through runoff from land that has been treated with pesticides, and even through skin contact with contaminated soil. A2013 studypublished in PloS ONE found that amphibians are vanishing at a rate of about 3.7 percent each year, which means that they will be absent from half of the habitats they currently occupy in about 20 years.

African Clawed Frog. Photo by Brian Gratwicke.

University of California, Berkeley researcher Tyrone Hayes, PhD, has found that male frogs with low dose exposure to endocrine (hormone) disrupting pesticides, such as the widely-used herbicide atrazine, experience inhibited growth of the larynx, have lower testosterone levels, and experience hermaphroditic changes.

The hermaphroditic changes range from males turning fully into females, to still being biologically male but having a loss of interest in reproduction and a lack of sperm, and sometimes even to mating with other males instead of females.

A 2014 study published in Environmental Pollution demonstrated that frogs accumulate measurable body burdens when exposed to soil that has been treated with pesticides such as imidacloprid, atrazine and fipronil.

In 2013, biologist Jason Rohr, PhD, studied the effects of atrazine on the immune system of amphibians and found that exposure to atrazine lowers immune functioning, leaving frogs susceptible to death from a certain fungal disease, Batrachochytrium dendrobatidis. This fungal disease, commonly known as chytrid fungus, is devastating amphibian populations across the world. Research has shown that the fungus has been in existence for a long time, but our changing world has created an environment that leaves amphibians vulnerable to the disease. As stated above, pesticides can play a large role in creating this vulnerability.

Researchers in Germanystudied two chemicals commonly used in orchards and on grains, and found a 100% mortality rate when frogs were exposed to doses recommended on the label.

The fungicide pyraclostrobin killed all of the frogs within an hour when applied at label recommended rates.

Dimethoate, a toxic systemic insecticide used on everything from asparagus and cherries, to tangerines and wheat, killed 40% of all frogs within a week of application.

In 2012, University of Pittsburgh researchers have found that the use of the weed killer Roundup, which contains the active ingredient glyphosate, in sub-lethal and environmentally relevant concentrations causes two species of amphibians to change their physiological shape by interfering with the hormones of tadpoles.

Economic Cost

Quinbi Village, Island of Matzu. Photo by Prince Roy.

Amphibians provide essential services for human society. They provide food provisioning services to humans and other wildlife, and have shown promise for medical use – secretions from frog skin have been shown to inhibit the transfer and spread of HIV. Some amphibians can inhibit the spread of mosquito-borne diseases through predation. They are prominent in some religions and mythology, providing cultural services. Finally, they are essential to regulating ecosystem structures, through nutrient cycling and the alteration of physical habitats. Unfortunately, it can be difficult to quantify how to put a number value onto ecological services, as there is not enough research to place a definitive economic value on all of these services that amphibians provide.

Litigation & Lawsuits

A federal district court approved a settlement in November 2013 requiring the U.S. Fish and Wildlife Service to better protect California red-legged frogs from seven common pesticides known to be highly toxic to amphibians. The settlement gave the agency two years to prepare biological opinions under the Endangered Species Act (ESA), to analyze pesticide use in and near the frog’s aquatic and upland habitats.